This invention relates to air conditioning systems for conditioning air in a plurality of areas or spaces in a common enclosure, and more particularly, relates to a control for regulating the operation of such system.
In recent years, many multi-zone buildings, such as schools, offices, apartments and hospitals have employed central station air conditioning systems to provide conditioned air to regulate the psychometric properties of the air in each of the zones of the building. One air conditioning system that has enjoyed widespread commercial success is known as a dual conduit system. A dual conduit system is designed to supply two air streams to enclosed areas or rooms that have a reversing transmission load; that is, during summer heat flows from the ambient and into the building, whereas during winter, heat flows from the building to the ambient. One air stream, called secondary air, is cooled the year round and is constant in temperature and variable in volume. Secondary air is a constant temperature-variable volume of air stream. The other air stream, called the primary air, is constant in volume and the air temperature is varied; it is warm in winter and cool in summer. Primary air is, therefore, a constant volume-variable temperature air stream. To obtain the two air streams, central station air conditioning apparatus is employed to provide the air temperature and volumes required.
The primary air conditioning apparatus varies the psychometric properties of the air supplied thereto, which may comprise a mixture of outdoor and return air or under some conditions, may comprise all return air. The apparatus includes filters to remove dirt or foreign matter entrained in the air, preheat coils as required to temper cold winter air, a humidifier to add winter humidification and a dehumidifier to remove excess moisture and to cool the supply air furnished at a constant volume to the enclosed areas within the building.
The secondary air conditioning apparatus also varies the psychometric properties of the air supplied thereto and supplies either/or all return air, a mixture of outdoor and return air, or all outdoor air, depending upon the season. The apparatus contains filters to remove dirt and foreign matter entrained in the air and a dehumidifier to remove excess moisture and/or to cool the supply air.
A refrigeration machine is necessary to complete the overall system. Any of the three basic refrigeration cycles, absorption, reciprocating, or centrifugal may be considered for the refrigeration equipment. Either chilled water from the refrigeration machine or direct expansion of refrigerant may be used to obtain the desired temperature for the supply air. The foregoing system is completely described in U.S. Pat. No. 2,609,743, issued Sept. 9, 1952, in the names of Carlyle M. Ashley and William T. McGrath.
Typically, the primary air supply is connected to an air conditioning terminal serving the peripheral portion of the enclosed area or room. The secondary air supply is connected to a terminal serving the interior portion of the room. The delivery of air to each of the two separate portions of the room may actually be accomplished via a single air conditioning terminal of the type disclosed in copending United States application Ser. No. 311,076, filed Dec. 1, 1972 now U.S. Pat. No. 3,867,980 in the name of Darwin G. Traver, and assigned to the same assignee as the assignee of the present application. Alternatively, the supply of conditioned air to the two separate portions of the enclosed area may be accomplished via two separate air conditioning terminals. The discharge of primary air is designed to offset transmission gains or losses; whereas the discharge of conditioned secondary air is designed to offset a relatively constant heating load created by lights, people, and machinery.
Heretofore, the supply of secondary air has been maintained completely independent from the supply of primary air. That is to say, there has been no interrelationship between the quantity of secondary air discharged into the space and the quantity of primary air discharged thereinto.
During the heating season, this lack of interdependence between the supply of primary air and secondary air has resulted in the simultaneous discharge of both relatively warm and cold air into the area. As is manifest, the foregoing is not desirable when conservation of energy and the reduction of operating costs are desired.
In order to prevent conditions from occurring wherein, in effect, the supply of conditioned secondary and primary air streams are "bucking" each other, it is desirable to control the quantity of primary air discharged inversely to the quantity of secondary air supplied into the space or area. For example, during the heating or winter season, designers and installers of systems of the type described, have assumed once the ambient temperature declined below a certain level, for example 50.degree. F, relatively warm primary air would always be required to offset transmission losses to the ambient through the peripheral walls of the building. However, there are times during winter operation, the presence of solar radiation will negate transmission losses to the ambient, thereby making the continued discharge of relatively warm primary air undesirable.
In effect, during the heating season, it is desirable to change the primary air system from a constant volume supply to a variable volume supply. Although separate thermostats may be employed to achieve the foregoing, the attendant increase in installation costs that would result from the duplication of thermostats would be undesirable, particularly where one of the thermostats would function only during the heating season. Additionally, with two separate thermostats, each thermostat may be separately set so that warm primary and cold secondary air may be simultaneously discharged. As noted heretofore, the simultaneous discharge of the separate air streams is undesirable, particularly when the conservation of energy is critically important.
Some system designers have attempted to compensate for solar radiation by employing devices to sense solar rays. Such devices are not always reliable, nor do they take into account the storage effect of the peripheral walls of the building. Thus, although there is always a time lag between the introduction or withdrawal of solar rays and the effect of such rays on transmission gains or losses, solar compensating devices do not take such time lag into consideration. Accordingly, the actual requirements of an area or space may be somewhat different than the theoretical requirements as determined by the absence or presence of solar radiation.